After Bishop Ryan of Buffalo, NY ordained him to the priesthood in 1886, Kozlowski first served as assistant to Ks. Jan Pitass at St. Stanislaus Parish (Buffalo, NY). Records also mention him as the priest who attended to the Poles in the Albany area before they organized their own parish in 1893. In 1889, Bishop Ryan assigned him to organize a new Polish parish in the Black Rock area – Assumption. During his tenure there, Kozlowski built the first combination structure for the parish.

In time, Kozlowski left Buffalo to answer the need for a Polish-speaking priest in Elmira, NY. There he accepted the pastorate of St. Casimir Parish. Upon his return to the Buffalo area, poor health caused him to serve as assistant in various parishes. Ks. Kozlowski died in Sisters of Charity Hospital in May 1922.